1. Field of the invention
The present invention relates to a medical X-ray image detecting device, more particularly to a device suited for detecting X-ray penetration images in a dental panoramic X-ray photographing apparatus.
2. Prior Art
Dental panoramic X-ray photographing apparatuses, which perform scanning by rotating an X-ray source and an image detecting device disposed in an opposed relation with each other along the dental arch of a patient while irradiating X-ray beams From the X-ray source, are widely used clinically to observe the arrangement of the teeth and the conditions of the dental roots of the patient.
Such X-ray panoramic photographing apparatuses are known as apparatuses capable of performing tomographing the curved section Formed along the dental arch to take the image of the dental jaw section of the patient on a single film so that the entire dental arch can be observed. In the case of these conventional apparatuses which expose X-ray penetration images to X-ray films, it is inevitably necessary to develop the X-ray films. In addition, after an image is taken along a tomographing route, it is impossible to obtain another image along a modified tomographing route. To solve these problems, a panoramic X-ray photographing apparatus has been developed recently, which obtains X-ray penetration images by using fluorescent light generated by a scintillator, introduces the light of the images into a solid-state image pickup device through an optical fiber bundle, and converts the images into electrical signals, then processes the signals so that panoramic tomographic images can be obtained, thereby reproducing the panoramic tomographic images on the display screen of a monitor unit.
In the case of the above-mentioned apparatus, the solid-state image pickup device has an image pickup surface size of about 5 mm square For example. This size is far smaller than the size of the fluorescent surface (6.times.150 mm for example) of the scintillator. It is very difficult to increase the size of image pickup surface of the solid-stale image pickup device. Even if possible, the cost is assumed to be excessive. Various methods have therefore been proposed to pick up visible light images formed on the fluorescent surface which is far larger than the image pickup surface of a solid-state image pickup device by using such a solid-skate image pickup device having a small image pickup surface.
Japanese Laid-open Patent Application No. 2-84942 has proposed a method, wherein the image on the fluorescent surface is contracted by using a tapered optical fiber bundle, [he input side area of which is as large as or half the area of the fluorescent surface of the scintillator and the output side area of which is as large as the area of the image pickup surface of the solid-stale image pickup device, and the image is input to the image pickup surface of the solid-state image pickup device.
In Japanese Utility Model Application No. 2-124689 (Japanese Laid-open Utility Model Publication No. 4-80507) and in its Foreign counterparts (U.S. Pat. No. 5,138,166, Ger. Pat. Application No. P41 38 659.0-35 and Fin. Pat. Application No. 915538), one of the applicants of the present invention has proposed an image detecting device which is characterized in that the fluorescent surface of a scintillator is divided in the vertical direction thereof into a plurality of rectangular units, the input end surface of each of the optical Fiber bundles of the device is attached to one of the divided rectangular surface units. the output end surface of each of the optical fiber bundles is attached to the image pickup surface of one of the image pickup devices, and the optical fiber bundles are distributed alternately right and left and laminated in the vertical direction.
In the case of the above-mentioned Japanese Laid-open Patent Application No. 2-84942, wherein the image on the Fluorescent surface of the scintillator is contracted by using the tapered optical fiber bundles and is transmitted to the image pickup surface of the solid-state image pickup device, the resolution of the image signal at the solid-state image pickup device is deteriorated because of a large image contraction ratio. Furthermore, it is difficult to taper (gradually reduce the diameter) the end of each element of the optical fiber so that the image can be contracted uniformly and significantly. Even if possible, production cost would be excessive.
Also, in the case of the above-mentioned Japanese Laid-open Utility Model Application No. 4-80507, wherein the fluorescent surface of the scintillator is divided in the vertical direction thereof into a plurality of rectangular units, a plurality (ten to several tens) of optical fiber bundles and solid state image pickup devices are necessary. It is complicated and troublesome to assemble these optical fiber bundles and image pickup devices (to attach the surfaces of the optical fiber bundles to those of the image pickup devices, for example). Production cost would also be excessive. Furthermore, since a plurality of solid-state image pickup devices are used, it is also complicated and difficult to adjust the sensitivity imbalance among the solid-state image pickup devices and to adjust the boundary regions of the solid-state image pickup devices.
As describe above, the conventional methods of introducing the light of the X-ray penetration image on the fluorescent surface of a scintillator via optical fiber bundles and picking up images by using solid-state image pickup devices having a small image pickup surface area have many problems.